1. Field of the Invention
The present invention relates to an endoscope channel switching apparatus which switches a communicating state of a channel part in an endoscope.
2. Description of the Related Art
Generally, an endoscope comprises an observation window to observe inside of a body cavity. If a body fluid sticks to the observation window, an observation field of view of the observation window narrows. Thus, in order to preserve the field of view, the endoscope is required to implement at least one of a gas supply and a water supply toward the observation window. The endoscope comprises a switching apparatus which switches from one of either the gas supply or water supply to the other. The switching apparatus comprises a piston and a cylinder. As the piston moves in relation to the cylinder, switching occurs from one to the other of the channel parts for gas supply or the channel parts for water supply.
Such an endoscope is disclosed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 9-122069. According to Jpn. Pat. Appln. KOKAI Publication No. 9-122069, a piston is provided with a hemispherical check valve part. The check valve part can be brought into tight contact with an inner circumference of a cylinder to increase airtightness between the piston and the cylinder. The check valve part has a ring shape. In addition, the inner circumference of the check valve part is joined to an outer circumference of the piston so as to allow the piston to penetrate the check valve part. As the piston moves in relation to the cylinder, switching occurs from one to the other of the channel parts for gas supply or the channel parts for water supply.